1. Field of the Invention
The invention relates in general relates to a coordinate positioning device and the method thereof, and more particularly, to an anti-noise coordinate positioning device and the method thereof.
2. Description of the Related Art
Coordinate positioning devices are widely applied in man-machine interface to facilitate the communication between the user and the electronic product. The coordinate positioning device, such as a mouse or a film positioning device for instance, detects the position and further has the position indicated on the screen by means of a cursor. The film positioning device, which includes two pieces of resistance-type films or capacitance-type films, detects the coordinates of the contact point touched by the user.
Referring to FIG. 1, a circuit diagram of a resistance-type film positioning device. Resistance-type film positioning device 100 includes a thin film 110. The thin film 110 further includes a thin film X and a thin film Y, wherein the thin film X and the thin film Y are plane resistances and have not any mutual contact in natural status. The resistance value on the thin film X changes along with the change of X-coordinate, not with the change of Y-coordinate, while the resistance value on the thin film Y changes along with the change of Y-coordinate, not with the change of X-coordinate. The thin film positioning device further includes transistors QX0, QX1, QY0, and QY1 as well as capacitances Cxp, Cxm, Cyp, and Cym for detecting the contact points and isolating the noises thereof. Of which, transistors QX0, QX1, QY0, and QY1 are controlled by signals X0, X1, Y0, and Y1.
When the user touches the film positioning device 100, the thin film X and the thin film Y will be connected at a contact point whose resistance is R_touch. On the thin film X, the resistance at points above the contact point is R_up, while the resistance at points below the contact point is R_down. On the thin film Y, the resistance at points to the left of the contact point is R_left, while the resistance at points to the right of the contact point is R_right. The thin film positioning device 100 will obtain the Y-coordinate of the contact point according to the ratio between R_up and R_down, and will obtain the X-coordinate of the contact point according to the ratio between R_right and R_left.
FIG. 2A is an equivalent circuit diagram for a thin film positioning device when detecting the X-coordinate of the contact point. When detecting the X-coordinate of the contact point, transistors QY0 and QY1 are switched on, allowing an electric current 11 to reach the ground via QY1, R_left, R_right, and QY0 in succession. After measuring the voltage at point XP, the ration between R_left and R_right will be obtained whereby the X-coordinate of the contact point can be obtained accordingly. Besides, the X-coordinate of the contact point can also be obtained after measuring the voltage at point XM.
FIG. 2B is an equivalent circuit diagram for a thin film positioning device when detecting the Y-coordinate of the contact point. When detecting the Y-coordinate of the contact point, transistors QX0 and QX1 are switched on, allowing an electric current I2 to reach the ground via QX1, R_up, R_down, and QX0 in succession. After measuring the voltage at point YP, the ration between R_up and R_down will be obtained whereby the Y-coordinate of the contact point can be obtained accordingly. Besides, the Y-coordinate at the contact point can also be obtained after measuring the voltage at point YM.
When applied in an electronic device, a thin film positioning device is likely to be coupled to plenty of noises which will cause errors to the coordinates obtained. For example, despite the user presses at the same contact point, however, due to the interference of the noise, the obtained coordinates of the contact point may be changeable. The general practice is to have multiple samplings of the contact point, say, 8 samplings, within a specific period of time, then use the average values of the 8 samplings as the coordinates of the contact point. However, using multiple sampling to determine the coordinates of the contact point is both time-consuming and energy consuming.